Stringer transition and method for producing composite parts using the same

ABSTRACT

A stringer comprises a base portion and first and second webs extending outwardly from the base portion. The orientation of at least one of the first and second webs may transition from a first angle to a second angle within an angle transition zone.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to co-pending U.S. application Ser. No.12/332,093 entitled COLLAPSIBLE MANDREL AND METHOD FOR PRODUCINGCOMPOSITE LAMINATES USING SAME filed on Dec. 10, 2008, the entirety ofwhich is incorporated by reference herein.

STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT

(Not Applicable)

FIELD

The present disclosure relates generally to the production of compositeparts and, more particularly, to a stringer configuration and method asused in forming composite laminates.

BACKGROUND

Composite structures are used in a wide variety of applications. Inaircraft construction, composites are used in increasing quantities toform the fuselage, wings, tail section and other components. Forexample, the wings may be constructed of composite skin members to whichstiffening elements such as stringers may be coupled to increase thebending strength and stiffness of the skin member. The stringers mayextend in a generally spanwise direction along the wing. The stringersmay be bonded to the skin members and may be configured to carry bendingloads or loads that are oriented substantially perpendicularly relativeto the skin member.

Stringers may be provided in a wide variety of cross-sectional shapes.For example, a stringer cross section may comprise a plurality ofcomposite plies formed in a hat-section configuration having a baseportion and a pair of webs extending outwardly from the base portion.The base portion may comprise a pair of flanges to facilitate coupling(e.g., bonding) of the stringer to the skin member such as the upper andlower wings skins of a wing. The hat-section stringer may include a capwhich interconnects the webs and encloses the hat section in order toincrease the torsional rigidity of the stringer. The cap also provideslateral stability to the webs against lateral bending or folding of thewebs. At an intersection of each one of the flanges with one of thewebs, a radius filler or noodle may be installed to enhance theload-carrying capabilities of the stringer.

The stringers in a wing may extend from an inboard section of the wingto an outboard section of the wing. Different loading conditions may beimposed on the wing at different locations along the wingspan. Forexample, at an inboard section of the wing, bending loads are typicallyhigher than bending loads at an outboard section of the wing. In orderto optimize the load carrying efficiency of the stringers and tominimize the occurrence of localized stresses in the skin members towhich the stringers are coupled, it is typically desirable to reduce thestiffness of the stringer at the outboard section of the wing where thestringer may terminate. One method of reducing the stiffness of thestringer is to remove a portion of the cap. Removal of the cap from thestringer may also provide an opening in the stringer through which fuelvapors may be vented. In this regard, the stringer may provide secondaryutility in addition to the primary load carrying function by acting as aconduit for venting fuel vapors from the inboard section of the wingnear the fuel tanks to the outboard section of the wings.

However, for stringer cross sections where the web is orientednon-perpendicularly relative to the base portion, removal of the cap maynecessitate a mechanism for maintaining the stability of the webs toprevent unwanted lateral bending. For example, the hat section of thestringer may comprise a cross-section having a trapezoidal configurationwherein each of the webs is angled inwardly toward one another and beinginterconnected by the cap. At locations where the cap is intact, the capstabilizes the webs against such lateral bending or folding. However, atlocations where the cap has been removed, the inwardly-angled webs areunsupported such that bending loads in the stringer may induce the websto fold laterally inwardly.

Stabilizing the webs against lateral bending may also be necessary forstringers having a biased configuration in the ply layup. Morespecifically, when the stringer is viewed in cross section at theintersection of one of the webs with one of the flanges, the quantity ofcomposite plies that make up the webs may be biased toward one side ofthe intersection or noodle. More specifically, when viewing a crosssection of the composite plies that make up a thickness of the web, alarger quantity of plies may be positioned on one side of theintersection or noodle than on an opposite side of the noodle. Thebiased configuration may have undesired results.

Current techniques for stabilizing the webs include the use of metal(e.g., aluminum) fittings which may be mechanically fastened to the websand flanges or skin members. Although generally satisfactory for theirintended purpose, the use of such fittings presents certain drawbacks.For example, each one of the metal fittings must be individuallyfastened to the stringer using specialized mechanical fasteners whichmay require the formation of appropriately-sized holes in the fiberreinforced composite material which makes up the stringer and skinmembers. As opposed to conventional methods of forming holes in metallicstructures, forming holes in composite materials and structures may alsorequire the use of specialized tooling.

In addition, composites structures may require the installation ofsleeved conductive fasteners. Such fasteners must typically be installedin a wet condition using a sealant to prevent galvanic corrosion betweenthe dissimilar materials of the metallic fitting and the compositestringer/skin member. The wet installation of fasteners may further berequired to prevent leakage across fasteners and/or to fill gaps betweenthe fastener and the hole to allow for proper shear load transfer acrossthe fastener and the hole. In addition, the use of metallic fittings mayrequire the installation of sealant at the mating surfaces of thefitting and the stringer/skin member to prevent moisture buildup. Evenfurther, in certain applications, fillet seals must be applied at theedges of the metallic fitting and the composite stringer to preventmoisture intrusion. As may be appreciated, the installation of metallicfittings in composite structures to stabilize the webs of a stringer mayresult in an increase in production time, increased part count, and anoverall increase in the complexity of the structure.

As can be seen, there exists a need in the art for a system and methodfor stabilizing the webs of a stringer against lateral bending orfolding which may otherwise occur as a result of a non-perpendicularorientation of the webs or due to a biased configuration in thecomposite plies that make up the stringer. Such stabilization may berequired at locations where a cap of the stringer is not provided orwhich may occur at locations along the stringer where the cap has beenremoved. In this regard, there exists a need in the art for a system andmethod for stabilizing the webs of the stringer against lateral bendingor folding which does not require the installation of separate metallicfittings.

SUMMARY

The above noted needs associated with composite stringers arespecifically addressed by the present disclosure which provides astringer having a base portion and first and second webs which extendoutwardly from the base portion. The orientation of the first web maytransition from a first angle to a second angle within an angletransition zone. Likewise, the orientation of the second web maytransition from the first angle to the second angle within the angletransition zone.

In an embodiment, the stringer may be incorporated into a compositeaircraft structure. The structure may include a skin member. Thestringer may be mounted to the skin member. The stringer may define across section that may transition from a hat section to a dual-bladesection. The first and second webs of the stringer may define anorientation relative to the base portion wherein the orientation maytransition within an angle transition zone which may have opposing firstand second angle zone ends. The first web may define a non-perpendicularorientation at the first angle zone end. Likewise, the second web maydefine a non-perpendicular orientation at the first angle zone end.

The present disclosure further includes a method of transitioning thestringer from the hat section to the dual-blade section. The method maycomprise the step of altering the orientation of the first web from thefirst angle to the second angle within the angle transition zone. Themethod may further comprise altering the orientation of the second webfrom the first angle to the second angle within the angle transitionzone.

In an embodiment, the method may comprise forming a base laminate bylaying up base plies on a base mold. The method may further includeincreasing a quantity of the base plies incrementally within the plytransition zone. In addition, the primary laminate may be formed bylaying up primary plies on a cure mold having cure mold side walls. Thecure mold side walls may transition from the first angle to the secondangle within the angle transition zone. The method may further comprisedecreasing the quantity of the primary plies incrementally within theply transition zone in correspondence with the incremental increase inthe base plies.

Furthermore, the method may comprise forming a wrap laminate by layingup wrap plies about a mandrel that may be formed complementary to thecure mold. The quantity of the wrap plies may be increased incrementallywithin the ply transition zone in correspondence with the incrementaldecrease in primary plies and the incremental increase in base plies. Inaddition, the method may comprise inserting the wrap laminate into theprimary laminate and placing a first and/or second noodle along the wraplaminate and primary laminate.

The method may also include adding the base laminate to the wraplaminate and primary laminate. Following the addition of the baselaminate to the wrap laminate and primary laminate, the method maycomprise co-curing the base laminate, wrap laminate and primary laminatetogether to form the stringer. The method may comprise forming anopening in the stringer by removing at least a portion of a cap of thestinger.

The features, functions and advantages that have been discussed can beachieved independently in various embodiments of the present disclosureor may be combined in yet other embodiments, further details of whichcan be seen with reference to the following description and drawingsbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the present invention will become moreapparent upon reference to the drawings wherein like numbers refer tolike parts throughout and wherein:

FIG. 1 is functional block diagram of a composite part such as astringer that may be formed of a base laminate, a wrap laminate and aprimary laminate;

FIG. 2 is a perspective illustration of an aircraft wing panel in anembodiment incorporating stringers extending from an inboard section toan outboard section of the wing panel;

FIG. 3 is a perspective illustration of one of the stringers of FIG. 2and illustrating the stringer being fastened to a skin member and havinga portion of a cap of the stringer being removed from the stringer;

FIG. 4 is an exploded perspective illustration of the stringer of FIG. 3illustrating the interconnectivity of the base laminate, the wraplaminate and the primary laminate that make up the stringer;

FIG. 5 is a cross-sectional illustration of the stringer taken alongline 5-5 of FIG. 3 and illustrating a base portion of the stringercomprising first and second flanges having first and second websextending upwardly therefrom and being interconnected by the cap andwherein the first and second webs may be oriented at a first angle;

FIG. 6 is a cross-sectional illustration of the stringer taken alongline 6-6 of FIG. 3 and illustrating the first and second webs beingoriented at a second angle which may be different than the first angleof the first and second webs as shown in FIG. 5;

FIG. 6A is a cross-sectional illustration of the stringer similar tothat which is illustrated in FIG. 6 and illustrating the first andsecond webs being oriented at a draft angle relative to a substantiallyperpendicular orientation of the first and second webs;

FIG. 7 is a cross-sectional illustration of the stringer taken alongline 7-7 of FIG. 3 and illustrating an increase in a thickness of thebase center interconnecting the first and second flanges as a result ofan increase in a quantity of wrap plies of the wrap laminate within aply transition zone;

FIG. 8 is a cross-sectional illustration of the stringer taken alongline 8-8 of FIG. 3 and illustrating the stringer having the cap removedfrom a portion thereof;

FIG. 9A is a plan view of the stringer along an angle transition zonewherein at least one of the first and second webs transitions from thefirst angle to the second angle;

FIG. 9B is a cross-sectional illustration of the stringer taken at thefirst angle zone end of the angle transition zone wherein at least oneof the first and second webs is oriented at the first angle;

FIG. 9C is a cross-sectional illustration of the stringer taken at thesecond angle zone end of the angle transition zone wherein at least oneof the first and second webs is oriented at the second angle;

FIG. 9D is a schematic illustration of the angle transition zone wherethe orientation of the first and second webs may vary in transitionrate;

FIG. 10 is a perspective illustration of the primary laminate flippedvertically relative to the orientation shown in FIG. 4 and illustratingthe incremental decrease in primary plies along the ply transition zonealong a direction from the inboard section to the outboard section ofthe primary laminate;

FIG. 11 is a perspective illustration of the wrap laminate flippedvertically relative to the orientation shown in FIG. 4 and illustratingthe incremental increase in wrap plies along the ply transition zone incorrespondence with the incremental decrease in primary plies;

FIG. 12 is a perspective illustration of the base laminate flippedvertically relative to the orientation shown in FIG. 4 and illustratingthe incremental increase in base plies along the ply transition zone incorrespondence with the incremental decrease in primary plies andincremental increase in wrap plies;

FIG. 13A is a reference cross section of the stringer in the plytransition zone;

FIG. 13B is a schematic illustration of the ply layup of the first andsecond flanges taken along line 13B-13B of FIG. 13A and illustrating thetransition from a biased configuration relative to a first noodle or abase-primary interface at a first ply zone end of the ply transitionzone to an unbiased configuration at the base-primary interface at asecond ply zone end of the ply transition zone;

FIG. 14A is a reference cross section of the stringer in the plytransition zone;

FIG. 14B is a schematic illustration of the ply layup of the first andsecond webs and cap taken along line 14B-14B of FIG. 14A andillustrating the transition from the biased configuration at aprimary-wrap interface at the first ply zone end to the unbiasedconfiguration at the primary-wrap interface at the second ply zone end;

FIG. 15A is a reference cross section of the stringer in the plytransition zone;

FIG. 15B is a schematic illustration of the ply layup of the base centertaken along line 15B-15B of FIG. 15A and illustrating the transitionfrom a first laminate thickness at the first ply zone end to a secondlaminate thickness at the second ply zone end;

FIGS. 16A-16B are reference cross sections of the stringer in the plytransition zone;

FIG. 16C is a chart illustrating a ply layup of primary plies, wrapplies and base plies;

FIG. 17A is a reference cross section of the stringer in the plytransition zone;

FIG. 17B is a chart illustrating a ply layup of the wrap plies and baseplies;

FIG. 18 is a partial sectional illustration of a first noodle orintersection of the base laminate, primary laminate and wrap laminate atthe first ply zone end of the ply transition zone and illustrating abiased configuration at the base-primary interface, the primary-wrapinterface and the wrap-base interface;

FIGS. 19-22 are partial sectional illustrations of the intersection ofthe base laminate, wrap laminate and primary laminate and illustrating asequence in transitioning from a biased configuration to an unbiasedconfiguration;

FIG. 23 is a partial sectional illustration of the intersection of thebase laminate, wrap laminate and primary laminate at the second ply zoneend of the ply transition zone and illustrating an unbiasedconfiguration;

FIG. 24 is a sectional illustration of the second noodle at a locationof the first angle zone end wherein the web is oriented at the firstangle relative to the base portion;

FIG. 25 is a sectional illustration of the second noodle at a locationof the second angle zone end wherein the web is oriented at the secondangle relative to the base portion;

FIG. 26 is a sectional illustration of the wrap laminate taken alongline 26-26 of FIG. 4 and illustrating lap splices of a portion of thewrap plies that make up the wrap laminate;

FIG. 27 is a perspective illustration of an aircraft which mayincorporate one or more stringers in a composite structure of theaircraft;

FIG. 28 is a methodology of forming a stringer transitioning from a hatsection to a dual-blade section;

FIG. 29 is a methodology of transitioning the stringer by altering theorientation of at least one of the first and second webs within theangle transition zone and/or altering the ply layup within the plytransition zone;

FIG. 30 is a flow diagram of an aircraft production and servicemethodology; and

FIG. 31 is a block diagram of an aircraft.

DETAILED DESCRIPTION

Referring now to the drawings wherein the showings are for purposes ofillustrating preferred and various embodiments of the disclosure onlyand not for purposes of limiting the same, shown in FIG. 1 is astructure 10 such as a composite part 24 which may comprise a stringer26 formed of a base laminate 54, a primary laminate 50 and a wraplaminate 58. The stringer 26 may include first and second flanges 36, 38which may be interconnected by a base center 40. The stringer 26 mayinclude a pair of first and second webs 30, 32 which may extendoutwardly from the first and second flanges 36, 38, respectively, andwhich may be interconnected by a cap 34. The first flange 36 mayintersect with the base center 40 and first web 30 at a first noodle 44.The second flange 38 may intersect with the base center 40 and thesecond web 32 at a second noodle 46. The base laminate 54 may becomprised of base plies 56 which may be formed of fiber reinforcedmaterial although any material may be used. The primary laminate 50 maybe formed of primary plies 52. The wrap laminate 58 may be formed ofwrap plies 60.

As can be seen in FIG. 1, the primary plies 52 may comprise at least aportion of the first flange 36, first web 30, cap 34, second web 32 andsecond flange 38. The wrap plies 60 may comprise at least a portion ofthe base center 40, first web 30, second web 32 and cap 34. The baseplies 56 may comprise at least a portion of the first flange 36, basecenter 40 and second flange 38. Each one of the first and second flanges36, 38 may be formed of a portion of the primary plies 52 and base plies56. The base center 40 may be formed of wrap plies 60 and base plies 56.Each one of the first and second webs 30, 32 may be formed of primaryplies 52 and wrap plies 60. Likewise, the cap 34 may be formed ofprimary plies 52 and wrap plies 60.

As described in greater detail below, the stringer 26 is configured suchthat at least one of the first and second webs 30, 32 transitions from afirst angle 110 as shown in FIGS. 5 and 9B to a second angle 112 asshown in FIGS. 6 and 9C within an angle transition zone 74 as shown inFIGS. 4 and 9A. In addition, as shown in FIGS. 10-12, a ply layup 48 ofthe first and second flanges 36, 38 and the base center 40 as well asthe ply layup 48 of the first and second webs 30, 32 and cap 34 maytransition within a ply transition zone 76. For example, in anembodiment, the stringer 26 may be provided in a hat section 84 as shownin FIGS. 5-7 which may be transitioned to a dual-blade section 86 asshown in FIG. 8 wherein the cap 34 may be at least partially removed asshown in FIG. 3. By transitioning the orientation of the first andsecond webs 30, 32 from the first angle 110 to the second angle 112and/or by altering the ply layup 48 of the stringer 26, the need forseparate fittings for stabilizing the webs may be eliminated.

For example, as shown in FIGS. 5-6, the system and method disclosedherein provides a means for transitioning a cross-section of thestringer 26 from one in which the first and second webs 30, 32 may beoriented in a non-perpendicular angle relative to the first and secondflanges 36, 38 as shown in FIG. 5 to a substantially perpendicular anglerelative to the first and second flanges 36, 38 as shown in FIG. 6.Optionally, as shown in FIG. 6A, the first and second webs 30, 32 maytransition to a non-perpendicular angle that is near perpendicular butwhich may include a draft angle 118 of up to five degrees or morerelative to a substantially perpendicular orientation to facilitateremoval of tooling following curing of the stringer 26. In addition, thesystem and method as disclosed herein provides a means for transitioninga ply layup 48 of the first and second flanges 36, 38, the first andsecond webs 30, 32 and the base center 40 from a biased configuration78, as shown in FIGS. 13B and 14B, wherein the quantity of plies may bebiased to one side of the first and second noodles 44, 46, to anunbiased configuration 80, as also shown in FIGS. 13B and 14B, whereinthe quantity of plies are generally uniformly distributed about thefirst and second noodles 44, 46 as will be described in greater detailbelow.

Referring to FIG. 2, shown is a structure 10 configured as an aircraft120, wing 124 having front and rear spars 18, 20 interconnected by aplurality of ribs 22 located at spaced intervals along a span of thewing 124. The structure 10 may include one or more stringers 26 whichmay be coupled to a skin member 12 for stiffening thereof. The stringers26 may, in turn, be interconnected to the ribs 22. As shown in FIG. 2,the stringers 26 may be configured as vent stringers 26 extending froman inboard 14 portion of the wing 124 to an outboard 16 portion of thewing 124. In this manner, the closed hat section 84 of the stringers 26may optionally function as a conduit for venting fuel vapors such asfrom fuel tanks which may be located at an inboard 14 portion of thewing 124. However, the stringer 26 may function to vent any number ofdifferent fluids without limitation or serve as a conduit for othersystems or elements. In this regard, each one of the stringers 26 may beprovided with an opening 88 wherein a portion of the cap 34 whichinterconnects the first and second webs 30, 32 may be removed. In suchan arrangement, the stringer 26 may transition from a hat section 84 toa dual-blade section 86.

Referring to FIGS. 3-8 and 10-14B, shown in FIG. 3 is a perspectiveillustration of one of the stringers 26 coupled to a skin member 12. Ascan be seen, the stringer 26 may include the angle transition zone 74wherein the orientation of at least one of the first and second webs 30,32 transitions from the first angle 110 as shown in FIG. 5 to the secondangle 112 as shown in FIGS. 6-8. Furthermore, FIG. 10 illustrates theply transition zone 76 wherein a ply layup 48 of the base portion 28 andthe first and second webs 30, 32 may transition from a biasedconfiguration 78 at the first ply zone end 106 as shown in FIGS. 13B and14B, to an unbiased configuration 80 at the second ply zone end 108 asalso shown in FIGS. 13B and 14B. In this regard, the ply transition zone76 comprises a location along the stringer 26 wherein the plies of thelaminates that interface with one another to form the stringer 26 areincrementally increased in one laminate in correspondence with anincremental decrease in the plies of the facing laminate. For example,referring briefly to FIG. 18, shown is an intersection of the baselaminate 54, wrap laminate 58 and primary laminate 50 wherein the baseplies 56, wrap plies 60 and primary plies 52 comprise the biasedconfiguration 78 at the first ply zone end 106 of the ply transitionzone 76. Referring briefly to FIG. 23, shown is the unbiasedconfiguration 80 of the base laminate 54, wrap laminate 58 and primarylaminate 50 at the second ply zone end 108 of the ply transition zone76. Advantageously, by incrementally increasing (i.e., adding) anddecreasing (i.e., dropping) plies within the ply transition zone 76, thestringer 26 can be morphed from the biased configuration 78 to theunbiased configuration 80.

Referring to FIG. 3, it should be noted that the stringer 26 may includeone or more angle transition zones 74 and/or one or more ply transitionzones 76 and is not limited to a single one of each. Furthermore, thepresent disclosure contemplates a stringer 26 configuration having onlyone or more ply transition zones 76 and not having an angle transitionzone 74. Conversely, the present disclosure contemplates a stringer 26configuration having only one or more angle transition zones 74 and nothaving a ply transition zone 76. Even further, the present disclosurecontemplates an arrangement wherein only one of the first and secondwebs 30, 32 of the stringer 26 includes the angle transition zone 74.The present disclosure also contemplates a stringer 26 configurationhaving only a single one of the first and second flanges 36, 38 andincluding only a single one of the first and second webs 30, 32extending outwardly from the single one of the first and second flanges36, 38.

Referring now to FIG. 4, shown is an exploded perspective illustrationof the base laminate 54, wrap laminate 58 and primary laminate 50 whichmake up the stringer 26 as shown in FIG. 3. In this regard, FIG. 4illustrates a configuration of each one of the laminates prior toassembling for co-curing or bonding to form the stringer 26. As can beseen, the location of the ply transition zone 76 of the primary laminate50 corresponds to the location of the ply transition zone 76 of the wraplaminate 58. Likewise, the ply transition zone 76 of the wrap laminate58 and primary laminate 50 correspond to the ply transition zone 76 ofthe base laminate 54. Even further, the angle transition zone 74 of thewrap laminate 58 corresponds to the angle transition zone 74 of theprimary laminate 50.

Referring to FIG. 5, shown is a sectional illustration of the stringer26 taken along line 5-5 of FIG. 3 and illustrating the orientation ofthe first and second webs 30, 32 at the first angle 110. As was earlierindicated, the first angle 110 transitions to the second angle 112 alongthe angle transition zone 74. As shown in FIG. 5, at least one of thefirst and second webs 30, 32 may define a non-perpendicular orientationat the first angle zone end 114 relative to the base portion 28. In anembodiment, each one of the first and second webs 30, 32 may be angledinwardly relative to one another at the first angle zone end 114. Inthis configuration, the hat section 84 of the stringer 26 defines atrapezoidal cross-sectional configuration. However, the stringer 26 maydefine any cross sectional configuration, without limitation, includingany closed cross sectional configuration.

Referring to FIG. 6, shown is a sectional illustration taken along line6-6 of FIG. 3 and illustrating an orientation of the first and secondwebs 30, 32 at the second angle zone end 116 of the angle transitionzone 74. In this regard, each one of the first and second webs 30, 32 isillustrated as defining a substantially perpendicular orientationrelative to the base portion 28 (i.e., relative to the first and secondflanges 36, 38). It should be noted that although the stringer 26 isillustrated as having a non-perpendicular orientation of the first andsecond webs 30, 32 at the first angle zone end 114 of the angletransition zone 74, the first and second webs 30, 32 may be orientedsubstantially perpendicularly relative to the base portion 28 at thefirst angle zone end 114. Likewise, although the first and second webs30, 32 are illustrated as defining a substantially perpendicularorientation at the second angle zone end 116 of the angle transitionzone 74, the first and second webs 30, 32 may define a non-perpendicularorientation relative to the base portion 28.

Even further, it is contemplated that the first and second webs 30, 32may transition from non-perpendicular orientations relative to the baseportion 28 or to different non-perpendicular orientations relative tothe base portion 28. Additionally, the present disclosure contemplatesan orientation of the first web 30 that is different than an orientationof the second web 32 at any point along the stringer 26 including at anypoint along the angle transition zone 74 of the first and second webs30, 32. However, for purposes of improving the stability of the firstand second webs 30, 32 at a location of the stringer 26 wherein the cap34 is removed, the first and second webs 30, 32 may be orientedsubstantially perpendicularly relative to the base portion 28.

Referring briefly to FIG. 7, shown is a sectional illustration takenalone line 7-7 of FIG. 3 and illustrating an increased thicknesst_(base center) of the base center 40 at the second ply zone end 108within the ply transition zone 76 as compared to the thicknesst_(base center) of the base center 40 at the first ply zone end 106. Theincreased thickness t_(base center) of the base center 40 is a result ofan incremental increase in the quantity of the wrap plies 60 and baseplies 56 within the within of the ply transition zone 76 as will bedescribed in greater detail below.

Referring briefly to FIG. 8, shown is a sectional illustration takenalone line 8-8 of FIG. 3 and illustrating a transition of the stringer26 from a hat section 84 to a dual-blade section 86. The dual-bladesection 86 may be formed by removing at least a portion of the cap 34along the length of the stringer 26 as is illustrated in FIG. 3. The cap34 may preferably be removed at a location outside of the ply transitionzone 76 and the angle transition zone 74 although removal of the cap 34may occur at any position along the length of the stringer 26.

Referring to FIGS. 9A-9D, shown in FIG. 9A is a plan view of thestringer 26 along the angle transition zone 74 wherein at least one ofthe first and second webs 30, 32 transitions from the first angle 110 tothe second angle 112. FIG. 9B is a cross-sectional illustration of thestringer 26 taken at the first angle zone end 114 wherein at least oneof the first and second webs 30, 32 may be oriented at the first angle110. FIG. 9C is a cross-sectional illustration of the stringer 26 takenat the second angle zone end 116 zone wherein at least one of the firstand second webs 30, 32 may be oriented at the second angle 112. FIG. 9Dis a schematic illustration of the angle transition zone 74 illustratingan embodiment of the stringer 26 wherein at least one of the first andsecond webs 30, 32 may vary in transition rate. For example, thetransition may initiate with the first and second webs 30, 32 beingoriented in a non-perpendicular relationship relative to the first andsecond flanges 36, 38. In an embodiment, the first and second webs 30,32 may be oriented at a 75 degree angle relative to the base portion 28although the first angle 110 may comprise any orientation relative tothe base portion 28 and is not limited to that which is illustrated.

Referring still to FIG. 9D, the transition from the first angle 110 tothe second angle 112 may include linear or non-linear angle transitionrates. For example, FIG. 9D illustrates an initial transition rate of0.17 degrees per inch of the first 6 inches of the angle transition zone74 in a direction from the first angle zone end 114 to the second anglezone end 116. The transition rate may increase to a higher rate ofchange such as the illustrated 0.20 degrees per inch transition ratewithin the next 10 inches of the angle transition zone 74. A moreaggressive transition rate such as the 0.32 degrees per inch transitionmay be provided within the next 28 inches of the angle transition zone74. The angle transition zone 74 may then provide for a gradualreduction in the transition rate. For example, the next 10 inches mayinclude a transition rate of 0.20 degrees per inch followed by atransition rate of 0.17 degrees per inch in the final 6 inches of theangle transition zone 74. As may be appreciated, the transition of thefirst angle 110 to the second angle 112 may comprise a non-lineartransition rate as indicated above although any combination of linearand non-linear translation rates may be incorporated into the angletransition zone 74. Furthermore, as was earlier mentioned, theorientations and transition rates of the first web 30 may be differentthan the orientations and transition rates of the second web 32 at anylocation along the stringer 26.

Referring to FIG. 10, shown is the primary laminate 50 in an orientationthat has been flipped vertically relative to the orientation of theprimary laminate 50 as shown in FIG. 4 in order to better illustrate aply layup 48 of the primary laminate 50 within the ply transition zone76. More specifically, FIG. 10 illustrates a plurality of primary plies52 which make up the primary laminate 50 and which are shown inexaggerated thicknesses in order to illustrate the incremental orstepwise decrease in the quantity of primary plies 52 from the first plyzone end 106 of the ply transition zone 76 to the second ply zone end108 thereof. FIG. 10 further illustrates the primary plies 52 of theprimary laminate 50 being disposed on a cure mold 100 such that theprimary ply 52 nearest the cure mold 100 assumes the shape of the toolsurface 68. The primary laminate 50 comprises at least a portion of thefirst and second flanges 36, 38 which collectively define the baseportion 28. Likewise, the primary laminate 50 comprises at least aportion of the first and second webs 30, 32. In this regard, the primarylaminate 50 is combined with the wrap laminate 58 as illustrated in FIG.11 to form the first and second webs 30, 32 and the cap 34 of thestringer 26 as will be described in greater detail below.

The primary laminate 50 may also include the angle transition zone 74wherein at least one of the first and second webs 30, 32 transitionsfrom the first angle 110 at the first angle zone end 114 as shown inFIG. 9B to the second angle 112 at the second angle zone end 116 asshown in FIG. 9C. The angle transition zone 74 is shown in FIG. 10 asbeing positioned in series relative to the ply transition zone 76.However, it is contemplated that the angle transition zone 74 and theply transition zone 76 may be placed in partial or complete overlappingrelationship relative to one another. In this regard, for a completelyoverlapping relationship of the angle transition zone 74 with the plytransition zone 76, the first and second webs 30, 32 transition from thefirst angle 110 to the second angle 112 simultaneous with the ply layup48 transitioning from the first ply zone end 106 to the second ply zoneend 108. However, for purposes of the present disclosure, the angletransition zone 74 is illustrated and described as being in series withand disposed adjacent to the ply transition zone 76. FIG. 10 furtherillustrates a succession of lap splices 72 wherein successive primaryplies 52 of the primary laminate 50 overlap one another as the quantityof primary plies 52 incrementally decrease or are dropped within the plytransition zone 76. In this regard, although FIG. 10 illustrates theprimary plies 52 being decreased or dropped along a bottom surface ofthe stringer 26, it is contemplated that the primary plies 52 may bedecreased or dropped along a top surface of the stringer 26.

Referring to FIG. 11, shown is the wrap laminate 58 comprised of anincrementally increasing quantity of wrap plies 60 corresponding to theincremental decrease or drop in the quantity of primary plies 52 of theprimary laminate 50 as shown in FIG. 10. More specifically, the lapsplices 72 of the overlapping wrap plies 60 are preferably positioned inregistration to the lap splices 72 of the incrementally decreasingprimary plies 52 as illustrated in FIG. 10. The wrap laminate 58 may beformed by laying up the wrap plies 60 about a mandrel 92 such as a foam98 mandrel or a bladder 96 which may be inflatable in order to permitremoval of the mandrel 92 following curing of the wrap plies 60.However, the wrap laminate 58 may be formed by laying up wrap plies 60about any suitable mandrel configuration and is not limited to foam 98or a bladder 96. The mandrel 92 may include mandrel side walls 93.Removal of the mandrel 92 following laying up and curing of the wrapplies 60 results in the formation of the vent surfaces 70 on theinterior side of the wrap laminate. The vent surfaces 70 maycollectively define an interior portion of the wrap laminate 58.

Referring to FIG. 12, shown is the base laminate 54 having a plytransition ramp 82 or ply transition zone 76 wherein the base plies 56are laid up on a mold line surface 69 of a base mold 90 and where thequantity of base plies 56 may be incrementally increased or added withinthe ply transition zone 76. As shown in FIG. 4 through 12, the layup ofthe primary plies 52, wrap plies 60 and base plies 56 is preferably inequal increments and in registration with one another such that therespective plies overlap with one another at the lap splices 72.However, the layup of the primary plies 52, wrap plies 60 and base plies56 may be in varying or unequal increments or in any suitable incrementalong the ply transition zone 76.

Referring to FIGS. 13A to 13B, shown is a layup of the primary plies 52to form the primary laminate 50 within the ply transition zone 76. Ascan be seen in FIG. 13B, the base laminate 54 defines a base-primaryinterface 62 with the primary laminate 50. The first and second flanges36, 38 transition from a biased configuration 78 at the first ply zoneend 106 to an unbiased configuration 80 at the second ply zone end 108as measured about the base-primary interface 62 as shown in FIG. 13A. Inan embodiment, the primary laminate 50 includes lap splices 72 betweensuccessive decreases or drops of the primary plies 52 of the primarylaminate 50 (or increases in the base plies 56 of the base laminate 54).Although a 0.75 inch lap splice 72 is illustrated and described in thepresent disclosure, the lap splice 72 may comprise any suitabledistance. For example, the lap splice 72 may comprise anywhere from 0.01inch or less to 2.0 inches or more between successive increases ordecreases in plies. In an embodiment, the lap splices 72 are preferablysized in proportion to a thickness of the plies. The length of the lapsplice 72 may be sized at a predetermined multiple of the thickness ofthe plies. For example, for a ply thickness of 0.0075 inch, a multipleof 100 may dictate a 0.75 inch lap splice. However, the lap splice 72may be provided in any length and a not limited to a given multiple ofthe thickness of the plies. Furthermore, the lap splices 72 may bearranged in any increment within the ply transition zone 76 includingequal increments, unequal increments, or varying combinations thereof.

Referring to FIGS. 14A to 14B, shown is an arrangement similar to thatwhich is shown in FIGS. 13A-13B wherein the cap 34 and the first andsecond webs 30, 32 comprise a biased configuration 78 at the first plyzone end 106 transitioning to an unbiased configuration 80 at the secondply zone end 108 as measured about the primary-wrap interface 64. As canbe seen in FIG. 14B, the incremental decrease in the quantity of primaryplies 52 of the primary laminate 50 is in correspondence with theincremental increase in wrap plies 60 of the wrap laminate 58 to formthe first and second webs 30, 32. FIG. 14B illustrates the lap splice 72in correspondence with the lap splice 72 illustrated in the first andsecond flanges 36, 38 and described above in FIG. 13B.

Referring to 15A to 15B, shown is the base center 40 comprised of wrapplies 60 of the wrap laminate 58 and base plies 56 of the base laminate54. As can be seen, the increase or adding of wrap plies 60 and theincrease or adding of base plies 56 results in an overall increase inthe thickness t_(base center) of the base center 40. For example andreferring briefly to FIGS. 6 and 7, shown in FIG. 6 is an initialthickness t_(base center) of the base center 40 at the first ply zoneend 106 of the ply transition zone 76. FIG. 7 illustrates an increasedthickness t_(base center) of the base center 40 at the second ply zoneend 108 as a result of the incremental increase in the quantity of wrapplies 60 and base plies 56. As can be seen in FIG. 15B, the wraplaminate 58 and base laminate 54 define the wrap-base interface 66. Inthe embodiment shown, the ply layup 48 of the wrap plies 60 and baseplies 56 is such that the base center 40 may have a first laminatethickness 136 at the first ply zone end 106 and a second laminatethickness 138 at the second ply zone end 108. However, the secondlaminate thickness 138 may comprise a greater quantity of wrap plies 60and base plies 56 as compared to the first laminate thickness 136.Furthermore, the second laminate thickness 138 may comprise an equalquantity or a reduced quantity of wrap plies 60 and base plies 56 ascompared to the first laminate thickness 136 depending, in part, uponthe initial quantity of plies in the wrap laminate 58 and base laminate54 at the first ply zone end 106 and/or depending on whether such pliesare increasing or decreasing in quantity within the ply transition zone76

Referring to FIGS. 16A-16C, shown in FIG. 16C is a chart illustrating aply layup 48 of the first and second flanges 36, 38 referenced in FIG.16A and which may correspond to a ply layup 48 of the first and secondwebs 30, 32 referenced in FIG. 16B. The chart illustrates an arrangementof fabric plies 102 and tape plies 104 of varying orientations and isprovided for illustration purposes only and is not to be construed aslimiting alternative ply arrangements. The chart illustrates a layupcomprising a fabric ply 102 of the primary laminate 50 disposed on thetool surface 68 followed by a layup of tape plies 104 oriented at 0degrees, plus 45 degrees, minus 45 degrees and 90 degrees, etc. Itshould be noted that the specific fiber orientations of the various wrapplies 60, primary plies 52 and base plies 56 may be provided in anyarrangement and may be optimized for a given set of manufacturing,environmental and/or static and dynamic loading conditions, etc. In thisregard, the arrangement of tape plies 104 and fabric plies 102 may beprovided in a variety of alternative patterns other than that which isshown in FIG. 16C.

However, FIG. 16C illustrates a feature of the present disclosurewherein the ply layup 48 of the primary plies 52, wrap plies 60 and baseplies 56 which make up the first and second flanges 36, 38 and the firstand second webs 30, 32 may transition from a biased configuration 78 atthe first ply zone end 106 to an unbiased configuration 80 at the secondply zone end 108. For example, in the biased configuration 78, the firstply zone end 106 on the left-hand side of the chart of FIG. 16Cillustrates the quantity of primary plies 52 that make up the primarylaminate 50 as being greater in number that the single wrap ply 60 andthe single base ply 56 which is illustrated as a fabric ply 102. In theunbiased configuration 80 at the second ply zone end 108 on theright-hand side of the chart of FIG. 16C, the quantity of primary plies52 are equal in number to the quantity of tape plies 104 which make upthe wrap plies 60 and base plies 56.

FIGS. 17A-17B illustrate a ply layup 48 of the base center 40 of thestringer 26 within the ply transition zone 76 wherein the ply layup 48transitions from a first laminate thickness 136 to a second laminatethickness 138 which may be increased in thickness as compared to thefirst laminate thickness 136. A can be seen, the ply layup 48 of thebase plies 56 may incrementally increase in correspondence with theincremental increase of the wrap plies 60. The ply layup 48 of the baseplies 56 as shown in FIG. 17B corresponds to the ply layup 48 of thebase plies 56 as shown in FIG. 16C. As may be appreciated, the specificply layup 48 of the base center 40 may be altered by altering the plylayup 48 of the wrap plies 60 or by altering the ply layup 48 of thebase plies 56. In this regard, although the base center 40 illustratesan arrangement wherein the base plies 56 mirror the wrap plies 60 aboutthe wrap-base interface 66, a non-mirrored arrangement may be provided

Referring to FIGS. 18 through 23, shown are enlarged sectionalillustrations of the intersection of the first web 30 with the firstflange 36 at the first noodle 44 and which may optionally mirror thearrangement at the intersection of the second web 32 with the secondflange 38. As can be seen, FIGS. 18 through 23 illustrate the transitionin the primary laminate 50 and wrap laminate 58 from a biasedconfiguration 78 at the first ply zone end 106 to an unbiasedconfiguration 80 at the second ply zone end 108, and the transition ofthe wrap-base interface 66 from a first laminate thickness 136 to asecond laminate thickness 138. For example, FIG. 18 illustrates across-section of the first web 30 with the first flange 36 prior to theinitiation of the transition of the ply layup 48. As can be seen, theply layup 48 of the primary plies 52 comprise a plurality of tape plies104 and a single fabric ply 102 on an interior side of the ply layup 48although the ply layup 48 may comprise alternative ply materials on theinterior side of the ply layup 48 and any number of alternative plymaterials laid over the initial ply. In this regard, FIG. 18-25 areillustrative of a sequence about which the ply layup 48 of the stringer26 may be transitioned and is not to be construed as limitingalternative ply arrangements of the stringer 26. The ply layup 48 of thewrap laminate 58 may comprise any number of ply materials. For example,the ply layup 48 may include the single fabric ply 102 as shown whichmay be laid up on a suitable mandrel 92 such as a bladder 96 or a foam98 mandrel 92. The base laminate 54 is shown also as comprising a fabricply 102 although any ply material may be used. As shown in FIG. 18, thestringer 26 may have the biased configuration 78 at the base-primaryinterface 62 and primary-wrap interface 64 at the first ply zone end114. FIG. 18 also illustrates the first laminate thickness 136 at thewrap-base interface 66.

FIG. 19 illustrates the initial ply transition wherein the fabric ply102 for the primary laminate 50 illustrated in FIG. 18 has been dropped.Simultaneously, a wrap ply 60 has been added to the wrap laminate 58 andto the base laminate 54. In this regard, the overall thicknesst_(flange) of the first flange 36 which is comprised of the baselaminate 54 and primary laminate 50 remains constant as does the overallthickness t_(web) of the first web 30. A lap splice 72 is formed at theprimary-wrap interface 64. Likewise, a lap splice 72 is formed at thebase-primary interface 62 and at the wrap-base interface 66. FIG. 19illustrates that the primary-wrap interface 64 comprises a lap splice 72formed of tape plies 104. However, as was indicated above, plies havingany fiber orientation may be used. Furthermore, it is also contemplatedthat in each ply transition and at each interface, the lap splices 72that occur within the ply transition zone 76 may comprise lap splices 72of tape plies 104 having differing fiber orientations.

Referring to FIG. 20, shown is a second ply transition wherein one ofthe primary plies 52 is dropped and a wrap ply 60 is added to the wraplaminate 58 while a base ply 56 is added to the base laminate 54. As canbe seen in FIG. 20, the ply transition zone 76 may be configured suchthat a combined thickness of the base laminate 54 and primary laminate50 is maintained as is the combined thickness of the wrap laminate 58and primary laminate 50. However, the combined thickness of the wraplaminate 58 and the base laminate 54 which form the base center 40increases in thickness by two plies. FIG. 21 illustrates a third plytransition wherein a primary ply 52 is dropped from the primary laminate50 while a wrap ply 60 and a base ply 56 are added to the wrap laminate58 and base laminate 54, respectively, resulting in an increase in thethickness t_(base center) of the base center 40 and maintaining athickness t_(flange) of the first flange 36 and thickness t_(web) of thefirst web 30. FIG. 22 illustrates a second to last transition of pliesof the ply transition zone 76 wherein a primary ply 52 is dropped and awrap ply 60 is added to the wrap laminate 58 and a base ply 56 is addedto the base laminate 54. In an embodiment, as illustrated, the stringer26 may comprise a fabric ply 102 extending along the mandrel 92 suchthat the fabric ply 102 forms the vent surface 70 of the stringer 26.

Referring to FIG. 23, shown is a last ply transition step within the plytransition zone 76 wherein fabric plies 102 are added along the firstnoodle 44. As can be seen, the ply layup 48 of the stringer 26 at thesecond ply zone end 108 provides an unbiased configuration 80 at thebase-primary interface 62 as well as at the primary-wrap interface 64.The wrap-base interface 66 transitions from a first laminate thickness136 as shown in FIG. 18 to a second laminate thickness 138 at the secondply zone end 108 as shown in FIG. 23. As was indicated above, FIG. 23illustrates an arrangement of plies including, namely, tape plies 104and fabric plies 102. However any arrangement of ply layups may beprovided and is not limited to that which is illustrated in the Figures.For example, fabric plies 102 and tape plies 104 may be positioned atany location within each of the ply layups of the wrap laminate 58, baselaminate 54 and primary laminate 50. Other ply materials may also beused in the ply layup 48.

Referring to FIGS. 24-25, shown is the first noodle 44 or radius filler42 illustrating a transition thereof within the angle transition zone 74in correspondence with the angle transition zone 74 of the stringer 26illustrated in FIGS. 5, 6, 9A and 9D. As can be seen in FIG. 24, thefirst noodle 44 transitions from the first angle 110 at the first anglezone end 114 shown in FIG. 9B to the second angle 112 as shown in FIG.25 at the second angle zone end 116 as shown in FIG. 9C. The secondnoodle 46 may include a similar transition to the first noodle 44 but inmirror image. The first and second noodles 44, 46 may be specificallyshaped or preformed to correspond to the changing orientation of thefirst and second angles 110, 112 within the angle transition zone 74.The first and second noodles 44, 46 may be formed by any suitable meansknown in the art and may include the use of woven fabric as material forthe first and second noodles 44, 46 and forming or cutting as requiredto fill the radius defined between the primary laminate 50, baselaminate 54 and wrap laminate 58.

Referring briefly to FIG. 26, shown is a cross-sectional illustration ofthe ply layup 48 of wrap plies 60 that form the wrap laminate 58. As wasearlier mentioned, the wrap laminate 58 may be formed by laying up thewrap plies 60 about a suitable mandrel 92. For example, FIG. 11illustrates the incremental increase in the quantity of wrap plies 60which are formed about the mandrel 92 within the ply transition zone 76and are preferably arranged in correspondence with the incrementaldecrease in the primary plies 52 and the incremental increase in thebase plies 56. In an embodiment illustrated in FIG. 26, the axiallyoriented lap splices 72 of the wrap plies 60 are preferably positionedto fall within the cap 34 of the stringer 26. However, it iscontemplated that the lap splices 72 may be positioned to fall withinthe first and second flanges 36, 38, within the base center 40 or anycombination thereof. Furthermore, the extent of overlap of the lapsplices 72 as shown in FIG. 26 may be in proportion to the total numberof wrap plies 60 that are added within the ply transition zone 76. Inthis regard, the spacing between the lap splices 72 as shown in FIG. 26is preferably evenly distributed across a width of the cap 34 which maybe defined as the distance between the first and second webs 30, 32 ofthe stringer 26. The spacing between the lap splices 72 may be linear ormay be non-linear and may vary at any portion across a width of the cap34. Furthermore, the spacing between the lap splices 72 may be uniformlydistributed along any one of the first 30 and second webs 32 or alongthe base center 40 or along any combination thereof.

Referring to FIG. 27, shown is a perspective illustration of an aircraft120 which may incorporate one or more of the stringers 26 as disclosedherein. As can be seen in FIG. 27, the aircraft 120 may comprise afuselage 122 having a pair of wings 124 and having a tail section 128which may include a vertical stabilizer 132 and horizontal stabilizers130 and which may further include control surfaces 126 and propulsionunits 134. The aircraft 120 as shown in FIG. 27 is generallyrepresentative of a variety of vehicles which may incorporate thestringer 26 as described herein. In this regard, the stringer 26 may beincorporated into any system, subsystem, assembly, application,structure 10 or vehicle including any marine, land, air and/or spacevehicle.

In an embodiment, the aircraft 120 as shown in FIG. 27 may incorporatestringers 26 in the fuselage 122 section and/or in the wing 124 sectionwherein the stringers 26 may be coupled to skin members 12 in order toform upper and lower surfaces of the wings 124. As was earlierindicated, such stringers 26 may provide dual functionality in ventingfuel vapors from an inboard 14 section of the wing 124 to an outboardsection thereof in addition to a primary load carrying capability of thestringers 26. In this regard, the present disclosure provides acomposite aircraft 120 structure 10 which may comprise a skin member 12having a stringer 26 mounted thereto and which transitions to a hatsection 84 as illustrated in FIGS. 5-7 to a dual-blade section 86 asillustrated in FIG. 8. As was earlier mentioned, the dual-blade section86 may be formed by removing at least a portion of the cap 34 along thelength of a stringer 26. The cap 34 may preferably be removed at anylocation outside of the ply transition zone 76 and the angle transitionzone 74. However, it is contemplated that removal of the cap 34 may beat any position and may occur within the ply transition zone 76 and/orwithin the angle transition zone 74.

Referring now to FIG. 28, shown is a methodology of forming the stringer26 having the base portion 28 and the pair of first and second webs 30,32 which extend outwardly therefrom as illustrated in FIGS. 1-8. In anembodiment, the methodology for forming the stringer 26 may compriseinitially forming the base laminate 54 which may include laying up thebase plies 56 on the base mold 90 in step 150 as illustrated in FIG. 12.Formation of the base laminate 54 may include incorporation of the plytransition zone 76 wherein the ply layup 48 of the base plies 56 thatcomprise the base portion 28 are altered as described above withreference to FIGS. 12-23. More specifically, the methodology maycomprise step 152 including increasing the quantity of the base plies 56incrementally within the ply transition zone 76 such that the thicknessof the base laminate 54 increases from the first ply zone end 106 to thesecond ply zone end 108 as best seen in FIG. 12.

Step 154 may comprise forming the primary laminate 50 by laying up theprimary plies 52 on the cure mold 100 as best seen in FIG. 10. Theprimary laminate 50 may comprise at least a portion of the first andsecond flanges 36, 38 and first and second webs 30, 32 which may beinterconnected by the cap 34. The cure mold 100 may include cure moldside walls 101 which transition from the first angle 110 at the firstangle zone end 114 to the second angle 112 at the second angle zone end116 where the first and second angles 110, 112 are defined relative tothe base portion 28 as best seen in FIGS. 5-6. In this regard, the curemold 100 may incorporate a changing angle of the cure mold side walls101 similar to that which is illustrated in FIG. 9A to 9D. Regarding theply layup 48 of the primary laminate 50, step 156 may comprisedecreasing the quantity of the primary plies 52 incrementally within theply transition zone 76. As was earlier mentioned, the incrementaldecrease or drop in the quantity of primary plies 52 that are laid up onthe cure mold 100 is preferably in correspondence with the incrementalincrease in the quantity of base plies 56 that are laid out in step 152.

Referring to FIG. 11, step 158 may comprise forming the wrap laminate 58by laying up the wrap plies 60 about a suitable mandrel 92 such as afoam 98 mandrel or an inflatable bladder 96 or other suitable mandrelconfiguration. As best seen in FIG. 11, the mandrel 92 includes mandrelside walls 93 that are formed complementary to the cure mold side walls101. More specifically, the cure mold side walls 101 transition from thefirst angle 110 to the second angle 112 within the angle transition zone74. Likewise, the mandrel side walls 93 transition from the first angle110 to the second angle 112 in correspondence with the transition of thecure mold side walls 101. For example, as described above with referenceto FIGS. 9A and 9D, in an embodiment, the transition from the firstangle 110 to the second angle 112 may occur at a varying transitionrate. However, a variety of alternative transition rates may beincorporated into the angle transition zone 74 such that the methodologyis not limited to that which is illustrated and disclosed in FIGS.9A-9D.

Regarding the transition of plies in the wrap laminate 58 shown in FIG.11, step 160 may comprise incrementally increasing the quantity of wrapplies 60 within the ply transition zone 76. The incremental increase inthe wrap plies 60 is preferably in correspondence with the incrementaldecrease or drop in the primary plies 52 and the incremental increase inthe base plies 56. For example, as shown in FIG. 4, the angle transitionzones 76 incorporated into each one of the base laminate 54, wraplaminate 58 and primary laminate 50 are preferably registered or alignedwith one another such that assembly of the wrap laminate 58 into theprimary laminate 50 results in registration of the lap splices 72relative to one another. Likewise, assembly of the base laminate 54 tothe combination of the wrap laminate 58 and primary laminate 50 alsopreferably results in registration of the lap splices 72. In thisregard, step 162 comprises assembling the stringer 26 by inserting thewrap laminate 58 into the primary laminate 50. For example, in anembodiment, formation of the stringer 26 may comprise installing thewrap laminate 58 as illustrated in FIG. 11 into the primary laminate 50positioned on the cure mold 100 as shown in FIG. 10. The mandrel 92 mayalso be installed in the wrap laminate 58 during step 162.

Step 164 may comprise placing at least one of the first and secondnoodles 44, 46 as shown in FIGS. 24 and 25 along the wrap laminate 58and primary laminate 50 such that the cross-sectional configuration ofthe first and second noodles 44, 46 corresponds to the wrap laminate 58and primary laminate 50 along the length of the stringer 26. Morespecifically, the first and second noodles 44, 46 are preferablyprovided with a cross-sectional configuration that includes the firstangle 110 at the first angle zone end 114 and the second angle 112 atthe second angle zone end 116. As was earlier indicated, the first andsecond noodles 44, 46 may be formed by any suitable means includingpultrusion, extrusion, hand layup or any other suitable forming process.

Step 166 in the methodology of forming the stringer 26 may compriseadding the base laminate 54 to the wrap laminate 58 and primary laminate50 after installation of the first and second noodles 44, 46. As wasearlier indicated, the ply transition zone 76 in the base laminate 54 ispreferably positioned in correspondence to the ply transition zones 76of the base laminate 54 and wrap laminate 58 such that the lap splices72 are in registration with one another. Following assembly, the baselaminate 54, wrap laminate 58 and primary laminate 50 may be integratedinto a unitary structure 10 by co-curing in step 168 through theapplication of a predetermined amount of pressure and/or heat for apredetermined period of time using any suitable curing or bondingprocess.

Step 170 may comprise forming the opening 88 in the stringer 26 betweenthe first and second flanges 36, 38 by removing at least a portion ofthe cap 34. For example, as shown in FIG. 3, the cap 34 may be removedat a location that is outside the ply transition zone 76 and the angletransition zone 74 although the cap 34 may be removed at any locationalong the stringer 26. The opening 88 may provide a means for reducingthe stiffness of the stringer 26 and for venting the stringer 26.

With reference now to FIG. 29, the present disclosure also includes amethodology for transitioning the stringer 26 from a hat section 84 to adual-blade section 86. As was earlier indicated, the stringer 26 maycomprise the base portion 28 including the first and second flanges 36,38 interconnected by the base center 40 as best seen in FIGS. 5-8. Thestringer 26 may further comprise the first and second webs 30, 32 whichmay extend outwardly from the base portion 28 and which may beinterconnected by the cap 34 which may extend at least partially along alength of a stringer 26.

Step 180 of the methodology comprises altering the orientation of atleast one of the webs of the stringer 26 from the first angle 110 to thesecond angle 112 within the angle transition zone 74. For example, asillustrated in FIGS. 5-6, at least one of the first and second webs 30,32 may be oriented at the first angle 110 which may be a nominal ornon-perpendicular angle relative to the base portion 28. At the secondangle zone end 116, at least one of the first and second webs 30, 32 maybe transitioned to the second angle 112 which may comprise asubstantially perpendicular orientation thereof relative to the baseportion 28 although the second angle 112 which may comprise anon-perpendicular orientation. The transition rate with which the firstand second webs 30, 32 transition from the first angle 110 to the secondangle 112 along the angle transition zone 74 may be linear ornon-linear. For example, as illustrated in FIGS. 9A to 9D and asdescribed above, the angle transition may comprise an initially mildtransition rate with an increasingly aggressive transition rate towardsa center of the angle transition zone 74. The transition rate may thenreduce from the center of the angle transition zone 74 to the secondangle zone end 116.

Step 182 may comprise altering the ply layup 48 of at least one of thefirst and second webs 30, 32 of the stringer 26. In addition, step 182may comprise altering the ply layup 48 of the base portion 28 includingthe first and second flanges 36, 38. The alteration of the ply layupsmay occur within the ply transition zone 76 as best seen in FIGS. 10-23and which illustrate the incremental decrease in the quantity of primaryplies 52 and the corresponding incremental increase in the quantity ofwrap plies 60 and base plies 56. More specifically, the methodology maycomprise dropping a primary ply 52 when adding a wrap ply 60 and a baseply 56. In an embodiment, the dropping of primary plies 52 and adding ofwrap plies 60 and base plies 56 may occur in any suitable increment suchas, without limitation, increments of approximately 0.01 inch toapproximately 2 inches or more. The step of altering the ply layup 48 ofthe base portion 28 and the first and second webs 30, 32 within the plytransition zone 76 may comprise transitioning from the biasedconfiguration 78 at the first ply zone end 106 to the unbiasedconfiguration 80 at the second ply zone end 108 as shown in FIGS. 13A-23and as described above. However, the stringer 26 may be configured suchthat the biased configuration 78 is provided at the first and second plyzone ends 106, 108.

Step 186 of the methodology of forming the stringer 26 may furthercomprise maintaining an essentially constant thickness t_(flange) of atleast one of the first and second flanges 36, 38, and at least one ofthe first and second webs 30, 32 as well as the thickness of the capt_(cap) within the ply transition zone 76. For example, as shown inFIGS. 18-23, the total quantity of plies in the primary laminate 50 andbase laminate 54 that make up the first flange 36 and the total quantityof plies in the primary laminate 50 and wrap laminate 58 that make upthe first web 30 may be maintained in equal number within the plytransition zone 76. However, it should be noted that the quantity ofplies 52, 56, 60 may be increased or decreased within the ply transitionzone 76. Furthermore, the lap splices 72 may result in an increase inthickness by one ply within the ply transition zone 76.

Step 188 of the method of forming the stringer 26 may comprise formingthe opening 88 in the stringer 26 by removing at least a portion of thecap 34 of the stringer 26 as best seen in FIGS. 2 and 3. Morespecifically, FIG. 2 illustrates a removal of at least a portion of thecap 34 in order to form the opening 88 in the stringer 26. As indicatedabove, the opening 88 may provide a means for venting the stringer 26and for reducing the stiffness of the stringer 26. In addition, removalof the cap 34 may facilitate a reduction in the overall mass or weightof the stringer 26.

Referring to FIGS. 30-31, embodiments of the disclosure may be describedin the context of an aircraft manufacturing and service method 200 asshown in FIG. 30 and an aircraft 202 as shown in FIG. 31. Duringpre-production, exemplary method 200 may include specification anddesign 204 of the aircraft 202 and material procurement 206. Duringproduction, component and subassembly manufacturing 208 and systemintegration 210 of the aircraft 202 takes place. Thereafter, theaircraft 202 may go through certification and delivery 212 in order tobe placed in service 214. While in service by a customer, the aircraft202 is scheduled for routine maintenance and service 216 (which may alsoinclude modification, reconfiguration, refurbishment, and so on).

Each of the processes of method 200 may be performed or carried out by asystem integrator, a third party, and/or an operator (e.g., a customer).For the purposes of this description, a system integrator may includewithout limitation any number of aircraft manufacturers and major-systemsubcontractors; a third party may include without limitation any numberof vendors, subcontractors, and suppliers; and an operator may be anairline, leasing company, military entity, service organization, and soon.

As shown in FIG. 31, the aircraft 202 produced by exemplary method 200may include an airframe 218 with a plurality of systems 220 and aninterior 222. Examples of high-level systems 220 include one or more ofa propulsion system 224, an electrical system 226, a hydraulic system228, and an environmental system 230. Any number of other systems may beincluded. Although an aerospace example is shown, the principles of thedisclosed embodiments may be applied to other industries, such as theautomotive industry.

Apparatus and methods embodied herein may be employed during any one ormore of the stages of the production and service method 200. Forexample, components or subassemblies corresponding to production process208 may be fabricated or manufactured in a manner similar to componentsor subassemblies produced while the aircraft 202 is in service. Also,one or more apparatus embodiments, method embodiments, or a combinationthereof may be utilized during the production stages 208 and 210, forexample, by substantially expediting assembly of or reducing the cost ofan aircraft 202. Similarly, one or more of apparatus embodiments, methodembodiments, or a combination thereof may be utilized while the aircraft202 is in service, for example and without limitation, to maintenanceand service 216.

Additional modifications and improvements of the present disclosure maybe apparent to those of ordinary skill in the art. Thus, the particularcombination of parts described and illustrated herein is intended torepresent only certain embodiments of the present disclosure and is notintended to serve as limitations of alternative embodiments or deviceswithin the spirit and scope of the disclosure.

1. A stringer, comprising: a base portion; and a first web and a secondweb extending outwardly from the base portion, the orientation of atleast one of the first and second webs transitioning from a first angleto a second angle within an angle transition zone.
 2. The stringer ofclaim 1 wherein: a ply layup of the base portion and the first andsecond webs transitions within a ply transition zone.
 3. The stringer ofclaim 2 wherein: the ply transition zone has opposing first and secondply zone ends; the ply layup of the base portion and the first andsecond webs transitioning from a biased configuration at the first plyzone end to an unbiased configuration at the second ply zone end.
 4. Thestringer of claim 1 further comprising: a cap interconnecting the firstand second webs.
 5. The stringer of claim 1 wherein: the base portionincluding first and second flanges, each one of the first and secondflanges being comprised of a base laminate having base plies and aprimary laminate having primary plies; each one of the first and secondwebs being comprised of the primary laminate and a wrap laminate formedof wrap plies.
 6. The stringer of claim 5 further comprising: a basecenter interconnecting the first and second flanges and comprising thewrap laminate and the base laminate.
 7. The stringer of claim 1 wherein:at least one of the first and second angles comprises anon-perpendicular orientation of at least one of the first and secondwebs relative to the base portion.
 8. The stringer of claim 1 furthercomprising: an opening formed between the first and second webs.
 9. Thestringer of claim 2 wherein: the angle transition zone and the plytransition zone are in series relative to one another.
 10. The stringerof claim 2 wherein: the angle transition zone and the ply transitionzone at least partially overlap one another.
 11. The stringer of claim 1wherein: at least one of the first and second webs and at least one ofthe first and second flanges has a constant thickness along a length ofthe ply transition zone.
 12. A composite aircraft structure, comprising:a skin member; and a stringer mounted to the skin member, the stringertransitioning from a hat section to a dual-blade section and including:a base portion; and a first web and a second web extending outwardlyfrom the base portion, the orientation of the first and second websrelative to the base portion transitioning within an angle transitionzone having opposing first and second angle zone ends, at least one ofthe first and second webs defining a non-perpendicular orientation atthe first angle zone end.
 13. The composite aircraft structure of claim12 wherein: a ply layup of the base portion and the first and secondwebs transitions within a ply transition zone having opposing first andsecond ply zone ends, the ply layup of the base portion and the websforming a biased configuration at the first ply zone end and an unbiasedconfiguration at the second ply zone end; the angle transition zone andply transition zone being located in series relative to one another. 14.The composite aircraft structure of claim 12 wherein: the second anglecomprises a substantially perpendicular orientation of at least one ofthe first and second webs relative to the base portion.
 15. Thecomposite aircraft structure of claim 12 further comprising: a capinterconnecting the first and second webs.
 16. The composite aircraftstructure of claim 12 further comprising: an opening formed between thefirst and second webs.
 17. The composite aircraft structure of claim 12wherein: the stringer and skin member comprise a portion of at least oneof the following: a fuselage, a wing, a tail section.
 18. A method oftransitioning a stringer from a hat section to a dual-blade section, thestringer having a base portion and first and second webs extendingoutwardly therefrom, the method comprising the step of: altering theorientation of at least one of the first and second webs from a firstangle to a second angle within an angle transition zone.
 19. The methodof claim 18 further comprising the step of: altering a ply layup of thebase portion and the first and second webs within a ply transition zone.20. The method of claim 18 wherein: at least one of the first and secondangles comprises a non-perpendicular orientation of at least one of thefirst and second webs relative to the base portion.
 21. The method ofclaim 19 wherein: the angle transition zone and the ply transition zoneare in series relative to one another.
 22. The method of claim 19wherein: the angle transition zone and the ply transition zone at leastpartially overlap one another.
 23. The method of claim 19 wherein eachone of the first and second webs is comprised of a primary laminateformed of primary plies and a wrap laminate formed of wrap plies, thestep of altering the ply layup of the base portion and the first andsecond webs comprising: dropping a primary ply from the primary laminateand adding a wrap ply to the wrap laminate.
 24. The method of claim 23wherein the base portion includes first and second flanges, the firstand second flanges being comprised of a base laminate formed of baseplies and the primary laminate formed of the primary plies, the step ofaltering the ply layup of the base portion and the first and second websfurther comprising: adding a base ply to the base laminate.
 25. Themethod of claim 19 wherein the ply transition zone has opposing firstand second ply zone ends, the step of altering the ply layup of the baseportion and the first and second webs comprising: transitioning from abiased configuration at the first ply zone end to an unbiasedconfiguration at the second ply zone end.
 26. The method of claim 19wherein the base portion includes first and second flanges, the step ofaltering the ply layup of the base portion and the first and second websfurther comprising: maintaining a constant thickness of the first andsecond flanges and the first and second webs within the ply transitionzone.
 27. The method of claim 25 wherein the stringer further includes acap interconnecting the first and second webs, the method furthercomprising the step of: forming an opening in the stringer by removingat least a portion of the cap.
 28. A method of forming a stringer havinga base portion and a pair of first and second webs extending outwardlytherefrom, the method comprising the steps of: forming a base laminateby laying up base plies on a base mold; increasing the quantity of thebase plies incrementally within a ply transition zone; laying up primaryplies on a cure mold having cure mold side walls transitioning from afirst angle to a second angle within an angle transition zone; forming aprimary laminate by decreasing the quantity of primary pliesincrementally within the ply transition zone in correspondence with theincremental increase in base plies; laying up wrap plies about a mandrelformed complementary to the cure mold; forming a wrap laminate byincreasing the quantity of wrap plies incrementally within the plytransition zone in correspondence with the incremental decrease inprimary plies and incremental increase in base plies; inserting the wraplaminate into the primary laminate; placing at least one of a first andsecond noodle along the wrap laminate and primary laminate; adding thebase laminate to the wrap laminate and primary laminate; co-curing thebase laminate, wrap laminate and primary laminate to form the stringer;and forming an opening in the stringer by removing at least a portion ofa cap of the stinger.